全文获取类型
收费全文 | 20966篇 |
免费 | 2361篇 |
国内免费 | 1218篇 |
专业分类
电工技术 | 1088篇 |
综合类 | 1201篇 |
化学工业 | 3507篇 |
金属工艺 | 3329篇 |
机械仪表 | 1008篇 |
建筑科学 | 476篇 |
矿业工程 | 262篇 |
能源动力 | 521篇 |
轻工业 | 4126篇 |
水利工程 | 177篇 |
石油天然气 | 286篇 |
武器工业 | 184篇 |
无线电 | 1782篇 |
一般工业技术 | 2760篇 |
冶金工业 | 1310篇 |
原子能技术 | 1460篇 |
自动化技术 | 1068篇 |
出版年
2024年 | 119篇 |
2023年 | 487篇 |
2022年 | 880篇 |
2021年 | 984篇 |
2020年 | 948篇 |
2019年 | 865篇 |
2018年 | 854篇 |
2017年 | 915篇 |
2016年 | 852篇 |
2015年 | 841篇 |
2014年 | 1108篇 |
2013年 | 1348篇 |
2012年 | 1335篇 |
2011年 | 1510篇 |
2010年 | 1015篇 |
2009年 | 1085篇 |
2008年 | 1014篇 |
2007年 | 1324篇 |
2006年 | 1127篇 |
2005年 | 953篇 |
2004年 | 874篇 |
2003年 | 729篇 |
2002年 | 551篇 |
2001年 | 465篇 |
2000年 | 388篇 |
1999年 | 345篇 |
1998年 | 270篇 |
1997年 | 235篇 |
1996年 | 203篇 |
1995年 | 145篇 |
1994年 | 130篇 |
1993年 | 132篇 |
1992年 | 96篇 |
1991年 | 71篇 |
1990年 | 58篇 |
1989年 | 58篇 |
1988年 | 33篇 |
1987年 | 23篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 43篇 |
1981年 | 23篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 5篇 |
1959年 | 5篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
从等离子体的基本特性出发,综述了等离子体技术在氨气合成、有机物合成、高分子合成以及纳米碳管的合成等方面的应用和最新进展,并展望了等离子体技术在化学合成方面的应用前景. 相似文献
62.
《Expert systems with applications》2014,41(1):105-125
Information systems (IS) facilitate organisations to increase responsiveness and reduce the costs of their supply chain. This paper seeks to make a contribution through exploring and visualising knowledge mapping from the perspective of IS investment evaluation. The evaluation of IS is regarded as a challenging and complex process, which becomes even more difficult with the increased complexity of IS. The intricacy of IS evaluation, however, is due to numerous interrelated factors (e.g. costs, benefits and risks) that have human or organisational dimensions. With this in mind, there appears to be an increasing need to assess investment decision-making processes, to better understand the often far-reaching implications associated with technology adoption and interrelated knowledge components (KC). Through the identification and extrapolation of key learning issues from the literature and empirical findings, organisations can better improve their business processes and thereby their effectiveness and efficiency, while preventing others from making costly oversights that may not necessarily be only financial. In seeking to enlighten the often obscure evaluation of IS investments, this paper attempts to inductively emphasise the dissemination of knowledge and learning through the application of a fuzzy Expert System (ES) based knowledge mapping technique (i.e. Fuzzy Cognitive Map [FCM]). The rationale for exploring knowledge and IS investment evaluation is that a knowledge map will materialise for others to exploit during their specific technology evaluation. This is realised through conceptualising the explicit and tacit investment drivers. Among the several findings drawn from this research, the key resulting knowledge mapping through FCM demonstrated the complex, multifaceted and emergent behaviour of causal relationships within the knowledge area. The principal relationships and knowledge within IS investment evaluation are illustrated as being determined by a blend of managerial and user perspectives. 相似文献
63.
人血浆蛋白C的纯化与鉴定 总被引:1,自引:0,他引:1
目的 建立人血浆蛋白C的纯化与鉴定方法。方法 利用DEAE SephadexA 5 0代替氯化钡 ,对血浆进行预处理 ,再经DEAE SepharoseFF离子交换和肝素 SepharoseCL 6B亲和层析进行分离纯化 ,用活化的部分凝血活酶时间 (APTT)测定组分活性 ,非还原型SDS PAGE测定其相对分子质量 ,Westernblot鉴定其特异性。结果获得相对分子质量为 6 2 0 0 0的蛋白条带 ,此条带可与人蛋白C单克隆抗体发生特异性反应。结论 已成功地从血浆中分离到蛋白C ,为其规模化生产奠定了基础。 相似文献
64.
65.
66.
67.
ExPosition is a new comprehensive R package providing crisp graphics and implementing multivariate analysis methods based on the singular value decomposition (svd). The core techniques implemented in ExPosition are: principal components analysis, (metric) multidimensional scaling, correspondence analysis, and several of their recent extensions such as barycentric discriminant analyses (e.g., discriminant correspondence analysis), multi-table analyses (e.g.,multiple factor analysis, Statis, and distatis), and non-parametric resampling techniques (e.g., permutation and bootstrap). Several examples highlight the major differences between ExPosition and similar packages. Finally, the future directions of ExPosition are discussed. 相似文献
68.
A new model to predict the adsorption equilibrium of mixtures containing supercritical components was presented. The difference in the adsorption mechanism between the supercritical components and the condensable components was accounted for in the new model. Lateral interaction in the adsorbed phase was also considered in the local isotherm. The new model was verified by the experimental data of the mixture CH4/CO2/C2H6 on activated carbon JX101 collected for 283-313 K and pressures up to . It was also verified with the experimental data published previously in literature. Considerable improvement in the prediction precision was achieved in using the new model to predict the adsorption of mixtures on activated carbon. 相似文献
69.
Dilip Chandra Ghimire Sudip Adhikari Hideo Uchida Masayoshi Umeno 《Diamond and Related Materials》2006,15(11-12):1792
We report the effects of gas composition pressure (GCP) on the optical, structural and electrical properties of thin amorphous carbon (a-C) films grown on p-type silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition (MW SWP CVD). The films, deposited at various GCPs ranging from 50 to 110 Pa, were studied by UV/VIS/NIR spectroscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and current–voltage characteristics. The optical band gap of the a-C film was tailored to a relatively high range, 2.3–2.6 eV by manipulating GCPs from 50 to 110 Pa. Also, spin density strongly depended on the band gap of the a-C films. Raman spectra showed qualitative structured changes due to sp3/sp2 carbon bonding network. The surfaces of the films are found to be very smooth and uniform (RMS roughness < 0.5 nm). The photovoltaic measurements under light illumination (AM 1.5, 100 mW/cm2) show that short-circuit current density, open-circuit voltage, fill factor and photo-conversion efficiency of the film deposited at 50 Pa were 6.4 μA/cm2, 126 mV, 0.164 and 1.4 × 10− 4% respectively. 相似文献
70.
Model epoxy and bismaleimide compounds in thin film form were used to simulate epoxy and bismaleimide composite surfaces, in order to study compositional changes and interfacial reactions induced by oxygen plasma treatment. X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IR-RAS) were used to probe chemical changes which occurred. XPS and IR-RAS were found to be complementary techniques in determining the nature of functional groups incorporated into surfaces by plasma treatment. IR-RAS analysis of the model surfaces following exposure to a liquid epoxy resin revealed that while adsorption of the liquid epoxy occurred on both plasma-treated and nonplasma-treated surfaces, the oxygen plasma-treated surface alone was capable of initiating ring-opening reactions in the epoxy. However, this effect was not observed unless immediate contact was made between the plasma-treated surface and the liquid epoxy resin, illustrating the short-lived reactivity of the functional groups on the plasma-treated surface. 相似文献